This invention relates to dishwasher controls and in particular to a dishwasher control for detecting the opening of the dishwasher door and thereupon disabling operation of the dishwasher. In particular this application relates to a very simple microprocessor based dishwasher control which has a single pole, single contact door switch and which eliminates the need for optical couplers, operational amplifiers and the like in connection with providing an input to the microprocessor of of the condition of the appliance door.
With the ready availability of microprocessors, appliance controls such as controls for dishwashers have widely incorporated microprocessors. When incorporated in such controls, the microprocessor receives inputs from various sensors and provides outputs to control the various operational elements of the dishwasher such as the pump, a water valve, detergent and wetting agent dispensers, heaters and the like. In order to provide an indication to the microprocessor that the dishwasher door is open while at the same time disabling the various operational elements, many prior art dishwashers have included two door switches, one of which directly disables the operational elements and the other of which is used to provide an indication input to the microprocessor that the door is open.
One problem with the use of two switches has been that, as more switch contacts are used and complexity increases, the likelihood of failure increases likewise.
Furthermore, since the microprocessor operates at low voltage and since the door switches are subject to line voltage, conventionally the input from the door switch to the microprocessor has been isolated electrically from the microprocessor by the use of optical couplers, operational amplifiers and the like. In order to accomplish input to the microprocessor with such circuitry various other electric components have also been utilized to achieve the desired isolation of the microprocessor from line voltage. Such components add undesired expense and complexity to dishwasher controls. Further, the microprocessor control has conventionally been grounded to the neutral side of the power source. This arrangement has required additional circuit components.
Accordingly, it is desired to provide a very simple dishwasher control wherein only a single door switch is used which provides both the function of disabling the dishwasher pump and the function of indicating to the microprocessor that the door is open. Furthermore, it is desired to provide such a dishwasher control which does not utilize isolation devices such as optical couplers, operational amplifiers and the like. Lastly, it is desired to provide such a control which is very simple and inexpensive.